Components for medical circuits

ABSTRACT

Condensation or “rain-out” is a problem in medical circuits and previous attempts to manage and/or prevent rain-out have resulted in relatively expensive and/or difficult to manufacture medical circuit components. The subject patent provides an improved medical circuit component for managing rain-out. In particular the component may be an improved breathing tube, or insufflation system limb comprising a helically corrugated tube preferably incorporating a heater wire.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national phase of International Application No.PCT/NZ2011/000111, filed Jun. 16, 2011, which claims priority fromUnited States Provisional Application No. 61/357333, filed Jun. 22,2010.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to components for medical circuits forconveying gases to and/or from a patient. In one particular aspect, theinvention relates to conduits and in particular to heated breathingtubes for use in an inspiratory and/or expiratory limb of a breathingcircuit. In another particular aspect the invention relates to a heatedtube for a surgical insufflation system.

2. Description of the Related Art

In assisted breathing, particularly in medical applications, gaseshaving high levels of relative humidity are supplied and returnedthrough flexible breathing tubes of a relatively restricted sizetypically between a range of approximately 10 mm to 25 mm diameter(covering both neonatal and adult applications). Such breathing tubesare ideally very light, resistant to kinking or pinching but also veryflexible to ensure the greatest performance and level of comfort for thepatient. The light weight of a breathing tube is very important toreduce any forces applied to the patient interface by the weight of thetube. Similarly, breathing tubes must be flexible and able to bendeasily to achieve a high level of patient comfort, which in turn canimprove patient compliance.

In medical applications, such as with assisted breathing, the gasesinhaled by a patient are preferably delivered in a condition havinghumidity near saturation level and at close to body temperature (usuallyat a temperature between 33° C. and 37° C.). Condensation or rain-outcan form on the inside surfaces of the breathing tubes as the highhumidity breathing gases cool and/or come into contact with therelatively cooler breathing tube surface. Breathing gases exhaled by apatient are usually returned fully saturated and flow through anexpiratory breathing tube. If the expired gas is allowed to cool as itpasses along an expiratory breathing tube, condensation or rain-out mayalso occur.

Similarly, Continuous Positive Airway Pressure (CPAP) systems orpositive pressure ventilation systems that provide patients sufferingfrom obstructive sleep apnoea (OSA) with positive pressure breathinggases, also use breathing tubes for delivering (or removing) inspiratory(and/or expiratory) gases.

Condensate forming in a breathing tube (either inspiratory orexpiratory) can be breathed or inhaled by a patient and may lead tocoughing fits or other discomfort. Condensation within a breathing tubemay also interfere with the performance of connected equipment andancillary devices and/or various sensors.

Attempts have been made to reduce the adverse effects of condensation byeither reducing the level of condensation, or providing collectionpoints for draining condensed liquid from the tubing component. Reducingthe condensation or rain-out has generally been achieved by maintainingor elevating the temperature above the dew point temperature of thebreathing gas to reduce the formation of condensation. This temperatureis typically maintained by a heater wire within the breathing tube,although the rain-out performance of these breathing tubes may not becomplete due to a number of factors. Further, previous methods ofheating the gases flow to reduce rain-out, typically result in heatedtubing that has been expensive and/or difficult to manufacture.Particularly, in ‘single use’ applications such as typically found inhospital applications, the manufacturing cost of breathing tubes iscritically important. It is highly desirable to even further reducerainout, while preferably maintaining a low production cost, forexample, by utilising a manufacturing method that is capable of highproduction speeds.

Similarly, during laparoscopic surgery with insufflation, it may also bedesirable for the insufflation gas (commonly CO2) to be humidifiedbefore being passed into the abdominal cavity. This can help prevent‘drying out’ of the patient's internal organs, and can decrease theamount of time needed for recovery from surgery. Even when dryinsufflation gas is employed, the gas can become saturated as it picksup moisture from the patient's body cavity. The moisture in the gasestends to condense out onto the walls of the medical tubing or dischargelimb of the insufflation system. The water vapour can also condense onother components of the insufflation system such as filters. Any vapourcondensing on the filter and run-off along the limbs (inlet or exhaust)from moisture is highly undesirable. For example water which hascondensed on the walls, can saturate the filter and cause it to becomeblocked. This potentially causes an increase in back pressure andhinders the ability of the system to clear smoke. Further, liquid waterin the limbs can run into other connected equipment which isundesirable.

In this specification where reference has been made to patentspecifications, other external documents, or other sources ofinformation, this is generally for the purpose of providing a contextfor discussing the features of the invention. Unless specifically statedotherwise, reference to such external documents is not to be construedas an admission that such documents, or such sources of information, inany jurisdiction, are prior art, or form part of the common generalknowledge in the art.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a component and/ormethod of manufacturing a component that will at least go some waytowards improving on the above or which will at least provide the publicand the medical profession with a useful choice.

In a first aspect the invention consists in a component comprising: ahelically corrugated tube wherein the corrugation profile comprisesalternating outer crests and inner troughs; and a heater wire associatedwith said outer crests.

Preferably said tube has a substantially uniform wall thickness.

Preferably said tube has a maximum wall thickness not exceeding 3 timesthe minimum wall thickness.

Preferably said outer crests correspond to a location of maximum innerradius and maximum outer radius of said tube, and said inner troughscorrespond to a location of minimum inner radius and minimum outerradius of said tube.

Preferably each said outer crest comprises a peak region, and the peakregions include local troughs comprising a small inward dip, and saidheater wire associated with said outer crests is located within saiddip.

Preferably said tube includes an outer sheath supported on said outercrests.

Preferably said outer sheath traps air between adjacent outer crests.

Preferably said outer sheath restrains said heater wire associated withsaid outer crests in said local trough.

Preferably said helically corrugated tube includes multiple helixcorrugations.

Preferably said component further comprises a heater wire associatedwith said inner troughs.

Preferably said inner troughs has a different heating density than saidheater wire associated with said outer crests.

Preferably said heater wire associated with said inner troughs has alower heating density than said heater wire associated with said outercrests.

Preferably said helically corrugated tube has a varying helix pitch.

Preferably said helically corrugated tube has a continuously variablehelix pitch.

Preferably said component is a conduit for use in at least part of theexhaust arm of an insufflation system.

Preferably said component is a breathing tube for use in a breathingcircuit.

Preferably said component is a catheter mount or tube for connection toa patient interface.

Preferably said tube is flexible as defined by passing the test forincrease in flow resistance with bending according to ISO 5367.

Preferably said tube is an extruded corrugated tube.

Preferably said tube is a breathing tube and is terminated by a firstconnector at an inlet and a second connector at an outlet, and whereinonly one gases passageway is provided the length between said inletconnector and said outlet connector.

Preferably said tube is a corrugation transition region wherein saidhelical corrugations transition to a substantially annular corrugationin the vicinity of said first and second connector respectively.

In a further aspect the invention consists in a component comprising: acorrugated tube wherein the corrugation profile comprises alternatingouter crests and inner troughs, and wherein said outer crests include apeak region, and the peak regions include local troughs comprising asmall dip.

Preferably said tube has a substantially uniform wall thickness.

Preferably said tube has a maximum wall thickness not exceeding 3 timesthe minimum wall thickness.

Preferably said outer crests correspond to a location of maximum innerradius and maximum outer radius of said tube, and said inner troughscorrespond to a location of minimum inner radius and minimum outerradius of said tube.

Preferably said tube includes an outer sheath supported on said outercrests.

Preferably said outer sheath traps air between adjacent outer crests andrestrains said heater wire associated with said outer crests in saidlocal trough.

Preferably said outer sheath further traps air in said local troughs.

Preferably said corrugated tube is a helically corrugated tube.

Preferably said helically corrugated tube includes multiple helixcorrugations.

Preferably said helically corrugated tube has a variable helix pitch.

Preferably said tube includes a heater wire therein.

Preferably said component is a conduit for use in at least part of theexhaust arm of an insufflation system.

Preferably said component is a breathing tube for use in a breathingcircuit.

Preferably said tube is flexible as defined by passing the test forincrease in flow resistance with bending according to ISO 5367.

Preferably said tube is an extruded corrugated tube.

Preferably said tube is a breathing tube and is terminated by a firstconnector at an inlet and a second connector at an outlet, and whereinonly one gases passageway is provided the length between said inletconnector and said outlet connector.

Preferably each end of said tube is a corrugation transition regionwherein said helical corrugations transition to a substantially annularcorrugation in the vicinity of said first and second connectorrespectively.

In a further aspect the invention consists in a method of forming acomponent comprising: extruding a tube; passing said extruded tube intoa corrugator and forming corrugations in said extruded tube having acorrugation profile comprising alternating outer crests and innertroughs; and wherein each said outer crest comprises a peak region, andthe peak regions include local troughs comprising a small inward dip.

Preferably said corrugations are helical.

Preferably said method further comprises a step of winding at least oneheater wire into said local trough.

Preferably said method further comprises applying an outer sheath oversaid component.

Preferably said step of applying said sheath comprises extruding asheath over said component.

Preferably said extruded tube has a substantially uniform wall thicknessat the time of corrugating.

Preferably said outer crests correspond to a location of maximum innerradius and maximum outer radius of said component, and said innertroughs correspond to a location of minimum inner radius and minimumouter radius of said component.

Preferably said helically corrugated component includes multiple helixcorrugations.

Preferably said method further comprises a step of winding at least oneheater wire into said inner troughs.

Preferably said heater wire associated with said inner troughs has adifferent heating density than said heater wire associated with saidouter crests.

Preferably said heater wire associated with said inner troughs has alower heating density than said heater wire associated with said outercrests.

Preferably said helically corrugated component has a varying helixpitch.

Preferably said helically corrugated component has a continuouslyvariable helix pitch.

Preferably said tube is flexible as defined by passing the test forincrease in flow resistance with bending according to ISO 5367.

Preferably said method further comprises terminating a first end with afirst connector, and terminating a second end with a second connector,and wherein only one gases passageway is formed between said firstconnector and said second connector.

Preferably said step of forming said corrugations includes forming atransition region at each end of said component, and wherein saidhelical corrugations transition to a substantially annular corrugationin the vicinity of said first and second connector respectively.

In a further aspect the invention consists in components as hereindescribed with reference to any one or more of the drawings except FIG.8.

The term “comprising” as used in this specification and claims means“consisting at least in part of”. When interpreting each statement inthis specification and claims that includes the term “comprising”,features other than that or those prefaced by the term may also bepresent. Related terms such as “comprise” and “comprises” are to beinterpreted in the same manner.

This invention may also be said broadly to consist in the parts,elements and features referred to or indicated in the specification ofthe application and/or statements of invention, individually orcollectively, and any or all combinations of any two or more said parts,elements features or statements of invention, and where specificintegers are mentioned herein which have known equivalents in the art towhich this invention relates, such known equivalents are deemed to beincorporated herein as if individually set forth.

The invention consists in the foregoing and also envisages constructionsof which the following gives examples only.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cut-away side view of a medical tube componentaccording to one embodiment of the invention for example a breathingtube or a limb of an insufflation system.

FIG. 2 is cross section view of the component of FIG. 1 showing apreferred corrugation profile.

FIG. 3 is a schematic illustration of one type of breathing circuit inwhich a component according to the invention can be used.

FIG. 4 is a schematic illustration of a patient and a humidifiedinsufflation system showing the inlet and exhaust limbs.

FIG. 5 is a schematic illustration of a preferred forming method formedical tubing.

FIG. 6 is a side view of a medical conduit showing one preferredcorrugation transition region and channels formed in the annular sealingrings to allow the heater wires to step over each annular ring as theytransition along the cuff region adjacent an end cuff portion (withouter sheath not shown).

FIG. 7 is a schematic view of a medical conduit showing the preferredcorrugation transition region of FIG. 6.

FIG. 8 is a side view of a prior art annular corrugated conduit withinternal spiral heater wire.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the field of medical circuits, and in particular breathing circuits(including anaesthetic circuits), condensation or rain-out can be aparticular problem where high humidity breathing gases come into contactwith the walls of a component at a relatively lower temperature.

With reference to FIG. 3 a humidified ventilation system is shown inwhich a patient 100 is receiving humidified and pressurised gasesthrough a patient interface 102 connected to a humidified gasestransportation pathway or inspiratory breathing tube 103. It should beunderstood that delivery systems could also be continuous, variable orbi-level positive airway pressure or numerous other forms of respiratorytherapy. The inspiratory tube 103 is connected to the outlet 104 of ahumidification chamber 105 which contains a volume of water 106. Theinspiratory tube 103 may contain a heater or heater wires (not shown)which heat the walls of the tube to reduce condensation of humidifiedgases within the tube. The humidification chamber 105 is preferablyformed from a plastics material and may have a highly heat conductivebase (for example an aluminium base) which is in direct contact with aheater plate 107 of humidifier 108. The humidifier 108 is provided withcontrol means or electronic controller which may comprise amicroprocessor based controller executing computer software commandsstored in associated memory.

In response to the user set humidity or temperature value input via dial110, for example, and other inputs, the controller determines when (orto what level) to energise heater plate 107 to heat the water 106 withinhumidification chamber 105. As the volume of water within humidificationchamber 105 is heated, water vapour begins to fill the volume of thechamber above the water's surface and is passed out of thehumidification chamber outlet 104 with the flow of gases (for exampleair) provided from a gases supply means or ventilator/blower 115 whichenters the chamber 105 through inlet 116. Exhaled gases from thepatient's mouth are returned to the ventilator via a return expiratorybreathing tube 130.

The ventilator 115 is provided with variable pressure regulating meansor variable speed fan 121 which draws air or other gases through blowerinlet 117. The speed of variable speed fan 121 is controlled byelectronic controller 118. It will be appreciated the patient interface102 could equally be a nasal mask, oral mask, oronasal mask, nasalprongs or full-face mask, etc.

However, there are also other competing requirements that should besatisfied by medical tubing in the field of the present invention. Forexample, it is preferable that breathing tubes for breathing circuitsare: resistant to crushing; resistant to restrictions in flow when bent(increased resistance to flow <50% when bent around a 1 inch cylinder);resistant to kinking; resistant to changes in length/volume underinternal pressure (compliance); resistant to leaking (<25 ml/min @610a); have low flow resistance (increase in pressure @ max. rated flow<0.2 kPa); electrically safe i.e.: sparks in the tubing can be extremelydangerous, especially in oxygen-rich environments such as oxygentherapy.

International standard ISO 5367:2000(E) (Fourth ed., 2000 Jun. 1) is oneexample of how some of these desirable parameters are measured andassessed, and the document is hereby incorporated into thisspecification in its entirety by reference. It is preferable thatcomponents of the invention meet or exceed some or all of thesestandards. In a most preferred embodiment components of the inventionmeet all of these standards.

Helically wound medical tube conduits including helical (or annular)reinforcing beads many times thicker than the tube wall thickness havebeen previously provided to improve crush resistance and to preventblocking while maintaining a flexibility enabling the component to bendeasily without kinking. However, these types of conduits are relativelydifficult and slow to manufacture, resulting in higher costs. In manymedical applications, breathing tube components are “single use” and arediscarded regularly. Therefore, cost is a very important considerationfor producing commercially viable products. Particularly for single usebreathing tubes, a substantially uniform wall thickness extruded andcorrugated tube is significantly cheaper and faster to manufacture andhas therefore typically been preferred (for example breathing tubesformed from an extruded tubular parison). However, the rain-outperformance has also typically been poorer. It is this type of extrudedand corrugated tube, having dimensions and mechanical propertiessuitable for medical use, to which the present invention relates.

In this specification, terms “medical circuit” and “breathing circuit”are used to indicate the general field of the invention. It is to beunderstood that a “circuit” is intended to include open circuits, whichdo not form a complete closed circuit. For example, CPAP systems usuallyconsist of a single inspiratory breathing tube between a blower and apatient interface. The term “breathing circuit” is intended to includesuch “open circuits”. Similarly, the term “medical circuit” is intendedto include both breathing circuits and insufflation circuits (which arealso typically “open”). Similarly, the term “medical tubing” is intendedto be read as flexible tubing suitable for use in the type of medicalcircuits described above connecting between components of a medicalcircuit and providing a gases pathway between components of a medicalcircuit.

Breathing Tubing

Medical tubing in the field of the present invention has a nominal boresize from approximately 10 mm to approximately 30 mm, and lengthsranging from approximately 300 mm to 2.5 m. In particular applicationssuch as medical tubing to connect to an interface component the tubingmay be significantly shorter (e.g. 50 mm to 300 mm). A catheter mountfor example, may have a length of approximately 80 mm. A catheter mountis a single lumen tube which in use will carry both inspiratory andexpiratory breathing gases to and from a patient respectively.

With reference to FIGS. 1 and 2, an extruded breathing tube 1 withcorrugations formed in a helical manner is shown. The corrugationscomprise a series of alternating outer crests 3 and inner troughs 4 withrespect to centre line 20. At the “peak” of each outer crest 3, is alocal trough 5 comprising a small (with respect to the amplitude of thecorrugations) inward dip in the peak. As a result, the “outer crest” 3is intended to denote a region comprising the local trough 5 and the twolocal peaks adjacent either side. The outer crest 3, corresponds to alocation of maximum inner radius 21 and maximum outer radius 22. Theinner trough 4, corresponds to a location of minimum inner radius 23 andminimum outer radius 24.

An electrical heating wire 2 is placed in direct external contact to thetube 1, and wound along the local trough 5 associated with the outercrests 3 of the helical corrugations. As a result, the tube wall in theregion of the peak of the outer crests 3 is heated directly. It has beenfound that a significant portion of heat lost occurs in the region ofthe outer crests 3 of a substantially uniform thickness corrugated tube,and therefore this has been found to be an effective location to applyheat in order to more efficiently reduce rain-out. Further, because theheater wire is associated with the exterior surface of the breathingtube, the gases flow through the conduit is not further disturbed by thepresence of a heater wire in the flow path. The heater wire 2, is of asmall diameter compared to the diameter of the tube.

In one embodiment, it is preferable that the heater wire 2 is formed inan electrical loop so that the electrical circuit starts and finishes atthe same end of the breathing tube 1, which can be attached to a medicalrespiratory device that provides power to the heater wire circuit.

Therefore a second strand of heater wire 7, is preferably provided inthe inner trough 4. The second strand of heater wire 7, may be part ofthe same heater wire 2 that has been looped back during manufacture.Alternatively, heater wire 7 may be a separate run of heater wire thatis subsequently joined to heater wire 2 after winding.

Other arrangements of the heater wire are possible as illustrated by thefollowing examples: two wires in tandem in each crest arranged in anelectrical (series) loop; two wires in tandem in each trough arranged inan electrical (series connected) loop; two wires in tandem in each crestand two wires in tandem in each trough arranged in two separateelectrical (series connected) loops; two wires in tandem in each crestand two wires in tandem in each trough arranged in a continuouselectrical (series connected) loop in an arrangement with two completereturn runs up and down the tube.

Attachment of electrical termination connectors and/or joining of theends of the wires to create a return loop (or loops if multiples aredesired) could be performed in a number of ways. These could includesoldering, crimp connection, insulation displacement connection (IDC)and resistance welded joints. These connection methods can beimplemented in various ways to achieve parallel, series or combinationsof these methods depending on the desired result.

In another preferred embodiment, the heater wire 2 (associated with theouter crest 3) may also be selected with different electricalcharacteristics to apply more heat to the crest of the tube, whencompared with heater wire 7 (associated with the inner trough 4). Forexample a higher heating density heater wire (e.g. higher resistance)may be used for the heater wire 2, than for the heater wire 7.

In another embodiment, the helical corrugations (either single ormultiple helix arrangements described later) may have a varying pitchalong the length of breathing tube. In this way because the heater wires2, and 7 if present are wound with the corrugation profile, they willalso have a varying pitch along the tube length. This results in varyingheating density along the tube thereby allowing more (or less) heat tobe applied to different regions of the tube as desired. For example ahigher heating density may be desired at the chamber end where(typically) the highest rainout occurs (for an inspiratory breathingtube). This is because the gas is typically fully saturated at thechamber outlet. The inspiratory tube is heated to increase the gastemperature along the tube, thereby decreasing the relative humidity(and potential for rainout) of the gas as it flows towards the patientend. Similarly, in an expiratory breathing tube, an increased heatingdensity may be desirable at the patient end of the tube and/or themachine end of the tube.

In a further preferred embodiment, a thin external sheath 8 is used tocover the tube and the heater wires 2, 7 to prevent them being dislodgedand to further prevent heat loss. The sheath 8 provides an insulatingbarrier by trapping air in the space between adjacent outer crests 3 andthe outer wall of the tube (in the region of the inner troughs 4). Thecrest region 3 including local trough 5, also provides improvedinsulation in the crest region where air is trapped in the space (ifany) between the sheath 8 and the local trough 5, because the conductionpathway where the sheath is in contact with the crests is reduced.

The sheath 8 may or may not contact and hold the heater wire in place.The sheath can be formed by for example; spiral wrapping a cling tapeover the outside or by feeding the mandrel through a cross-head die 11and extruding a thin flexible plastic sheath 8 over the top as shown inFIG. 5. The sheath has the added benefit of improving compliance, (i.e.:reducing longitudinal stretch), pull strength, resistance to flow withbending and crush resistance, although it is important that the overallproduct still remains flexible to ensure adequate patient comfort etc.It will be appreciated that if an extruded sheath is employed, it may beable to be bonded securely to the tube during the extrusion process.This may have benefits in improving the torsional resistance of the tubeand limit the effects of a torsional “worming” action that can occurwith a spiral formed tube when experiencing a pulsing pressure astypically experienced in a breathing circuit.

The sheath 8, may be of the same material (or same base material) as thebreathing tube, particularly for embodiments where bonding between thesheath and tube or between the sheath and breathing tube end connectorsis desired. Bonding, if any, may be from residual heat in the sheath asit is formed over the breathing tube, and/or auxiliary heating/weldingprocesses may be employed. Alternatively, the sheath 8 may be of adifferent material, and a bonding agent may be applied if bonding isdesired.

In a further alternative embodiment, the tube of FIG. 2 including outersheath 8 may be provided without any heater wires. In this embodimentimproved insulation results from the crest region where air is trappedin the space between the sheath 8 and the local trough 5. Further, thehelical corrugations also improve mixing of the flow in the tube andreduce rainout. It has been found that the performance of this unheatedembodiment is superior to an unheated sheathed conduit of conventionalannular corrugation form such as illustrated in FIG. 9 (sheath notshown). It has also been found that the performance of an internallyheated embodiment of the conduit utilising a corrugation form with a dipin the crest and an external sheath, is superior to an internally heatedsheathed conduit of conventional corrugation form such as illustrated inFIG. 9 (sheath not shown).

It will be appreciated that other reinforcing processes may also be usedto supplement the tube in order to improve its performancecharacteristics still further (such as compliance, pull strength,resistance to flow with bending and crush resistance). Those processesmay or may not be integrated with the tube forming process.

In a further embodiment, the helical corrugations may be formed in amultiple start arrangement comprising a plurality of helicalcorrugations (i.e. a double helix incorporating two crests and twotroughs per pitch etc.). With this configuration, shown in FIG. 5,spiral winding of more than one pair of heater wires 2, 7 can beachieved per revolution. For example:

a double helix with heater wire in the crests (only) arranged in anelectrical (series) loop

a double helix with heater wire in the troughs (only) arranged in anelectrical (series connected) loop

a double helix with a wire in each crest and a wire in each trough (twoof each per pitch) arranged in two separate electrical (seriesconnected) loops. This can be achieved by creating two “crest to trough”linked circuits or a “crest to crest” and a “trough to trough” linkedcircuit. In the case of the latter arrangement, separate electricalcontrol of the heating of crests and troughs would be possible.

a double helix with a wire in each crest and a wire in each trough (twoof each per pitch) arranged in a single (series connected) electricalloop. This can be achieved by connecting appropriate adjacent crest andtrough wire ends to form an arrangement with two return runs.

a double helix with a wire in each crest and a wire in each trough (twoof each per pitch) arranged in a parallel-series connected electricalloop. This can be achieved by connecting adjacent crest and trough wireends into two pairs at the chamber end with appropriate terminationssuch as pins to accept a plug to allow subsequent connection to thepower supply. This would form one end of two separate parallel connectedpairs. At the patient end, all the wire ends can be linked together in acircumferential loop. This then links the patient ends of the parallelpairs (completing the two parallel loops) and also connects the ends ofthe two parallel pairs in series to complete the circuit return run.

a double helix with two wires in tandem in each crest and two wires intandem in each trough. This would allow multiple combinations ofseparate or linked circuits connected in series, parallel,parallel-series or series-parallel to provide various winding andtermination options for production or to achieve heating or controlbenefits.

Other multiples of helixes per pitch with associated pairs of wires(including tandem wires in each groove) can be employed in a similarfashion with more complex connection options.

Attachment of electrical termination connectors and/or joining of theends of the wires to create (a) return loop(s) could be performed in anumber of ways as described earlier.

The multi-helix arrangement will also reduce the time required to windthe heater wires during manufacture, since the maximum rpm of thewinding equipment is limited by balance issues, wire feed speed andsafety. Winding multiple wires simultaneously, allows more wire to bewound at any given winding speed. A further benefit arises by increasingthe number of breathing tubes (continuous production length) that can beproduced before changing reels of heater wire. These benefits directlyenhance the throughput of each production line.

The winding process can be performed in a number of ways depending onthe desired connection devices and tube handling method(s).

Reverse-Looped Spiral Heating Filament.

In this embodiment, the wire(s) is (are) wound onto the tube in onedirection, and then looped around (for example on the patient end of thetube) before winding back along the tube to the starting point tocomplete the loop. Tube handling for this method is best performed bycutting the continuous output from the corrugator into individual tubes,loading them onto mandrels and transferring the mandrels onto a windingmachine. The winding machine may have several stations that rotate themandrels and spiral the wire onto the tube, reversing at the end beforewinding back along the tube to complete the circuit. The loose ends atthe chamber end could be retained, for example with a clip system or byhot melt glue or similar adhesive. Once the wire winding is complete,the tube can be sheathed (if desired) to cover and retain the wire.

Pre-looped Spiral Heating Filament.

In this embodiment, the wire(s) is (are) pre-loaded onto an accumulatorsystem and doubled over complete with a loop in the middle ready fortransfer onto the tube. The wire loop(s) is (are) wound onto theaccumulator drum in one direction, then back to the other end forexample. The winding onto the tube is therefore performed in onedirection only. This can either be done on a separate mandrel system asper the previous option or it could be performed in-line direct off thecorrugator. The advantages of spiralling on-line eliminate the mandrelsand associated handling equipment. Once wire is loaded, the tubing canbe routed through a cross-head die for sheathing (if desired) as shownin FIG. 5 for example.

Paired Heating Filaments with Joints at One End (e.g. at the PatientEnd)

In this embodiment, corrugated joined tubes pass directly from thecorrugator through a joiner/winder assembly. This joins the ends ofpairs of wire strands together, then positions them over the corrugationspiral and may require further securing with for example, hot melt glueor UV curing adhesive, or a retaining clip. The winder head then rotatesaround the tube and applies paired runs of wire from separate spools atthe same time. The number of wire pairs to suit the number of helixesper pitch and the desired wire arrangements. The over-sheath (ifdesired) is subsequently fitted, and then the tubes are separated at thecuffs. Finally, the cuff fittings and end terminations are fitted.

In this alternative embodiment, the pairs of wires could be continuouslyspiraled around the tube and joined with a crimp connector without firstcutting the wires. The over-sheath is subsequently fitted, and then thewires are cut after the tubes are separated at the cuffs. Finally, thecuff fittings and end terminations are inserted.

Paired Heating Filaments Continuously Wound On-Line

In this embodiment, corrugated joined tubes pass directly from thecorrugator through a winder assembly. The winder heads rotate around thetube and apply paired runs of wire from separate spools at the sametime. The number of wire pairs to suit the number of helixes per pitchand the desired wire arrangements. The wires may require securing withfor example hot melt glue or UV curing adhesive or a retaining clip atthe ends of the tubing to prevent unraveling once the tubes areseparated. The over-sheath is subsequently fitted (if required), thetubes are separated and then the wires terminated via an appropriatemethod in a final assembly operation. This allows for a continuouswinding process with the rotational speed of the winding heads largelyconstant. Feed rate can vary as required to suit the pitch of thegrooves at the section of the tube being wound.

Testing has demonstrated the performance improvements of the presentmedical tubing, compared to prior art breathing tubes comprising anannular corrugated tube having an internal spiral heater wire such asshown in FIG. 8 for example.

In further embodiments it is envisaged that the helical corrugations mayalso carry conductor(s) for sensors located somewhere along the tubei.e. temperature, humidity, flow or pressure sensors etc. Theseconductors may share a local trough 5 (and/or inner trough 4) in commonwith a heating wire or may be formed as an additional helix run with aseparate local trough 5 (and/or inner trough 4). This would remove theneed for a separate loose cable thereby reducing complexity of setup andassociated clutter around the patient. Alternatively, one or more heaterwires may be used to also carry signal from a sensor or transducer.

With reference to FIG. 5, the preferred process used to make medicaltubing involves extruding a molten tubular profile 12 into a corrugatormachine 13 utilising an endless chain of mould blocks 14 to form aflexible helically corrugated tube 15. An extruder 16 such as a Welexextruder equipped with a 30-40 mm diameter screw and typically a 12-16mm annular die head with gap of 0.5-1.0 mm has been found to be suitablefor producing low cost tubes quickly. Similar extrusion machines areprovided by American Kuhne (Germany), AXON AB Plastics Machinery(Sweden), AMUT (Italy), Battenfeld (Germany and China).

A corrugator such as those manufactured and supplied by Unicor®(Hassfurt, Germany) has been found to be suitable for the corrugationstep. Similar machines are provided by OLMAS (Carate Brianza, Italy),Qingdao HUASU Machinery Fabricate Co., Ltd (Qingdao Jiaozhou City, P.R.China), or Top Industry (Chengdu) Co., Ltd. (Chengdu, P.R. of China).

During manufacture, the molten tube 12 is passed between a series ofrotating moulds/blocks 14 on the corrugator after exiting the extruderdie head 16 and is formed into a corrugated tube such as thatillustrated in FIGS. 1 & 2 for example. The molten tube is formed byvacuum applied to the outside of the tube via slots and channels throughthe blocks and/or pressure applied internally to the tube via an airchannel through the centre of the extruder die core pin. If internalpressure is applied, a specially shaped long internal rod extending fromthe die core pin and fitting closely with the inside of the corrugationsmay be required to prevent air pressure escaping endways along the tube.

The tube 1 has a wall 6 that is preferably between approximately 0.3-1mm thick for a breathing tube of typical dimensions (i.e. betweenapproximately 10 mm and 30 mm diameter for neonatal and adultapplications respectively and approximately 1-2 meters in length).

With reference to FIG. 8, a typical prior art medical conduit includes aplain cuff region 9 for connection to an end connector fitting 10.Similarly, the end connector fitting of the present tube is preferablyof a standard type (for example, the end connector may be plastic andincorporate a medical taper) according to the intended use of themedical tubing and is preferably permanently fixed. Fixing methods mayinclude friction fit, adhesive bonding, over moulding, or thermal orultrasonic welding etc.

One advantage of the preferred type of tube manufacture described abovewith reference to FIG. 5, is that some of the mould blocks 14 caninclude end cuff features that are formed at the same time as thetubing. Manufacture speeds can be significantly increased by thereduction in complexity and elimination of secondary manufacturingprocesses. While this method is an improvement over separate cuffforming processes, a disadvantage of the prior art plain cuff is thatthe corrugator must slow down to allow the wall thickness of the tube inthis area to increase (the extruder continues at the same speed). Thecuff thickness is increased to achieve added hoop strength and sealingproperties with the cuff end connector or adaptor fitting. Further, theheat of the molten plastic in this thicker region is difficult to removeduring the limited contact time with the corrugator blocks and this canbecome an important limiting factor on the maximum running speed of thetube production line.

With particular reference to FIGS. 6 & 7, the end cuff region of thepresent medical tube (17+18+9) is formed at the same time as thespiral/helical corrugations, and is configured to receive an endconnector adapter fitting 10 (not shown). Also, to facilitate theconnection and wire routing between the spiral corrugation region oftube 1 (i.e. left hand side of conduit shown), and the annular cuffcorrugation sealing region 18, a transition region 17 may be provided.The region 17 transitions from the helical corrugation profile to amostly annular corrugation profile adjacent the open cuff end 9. Theannular region 18 provides a better seal between the exterior surface ofthe cuff adaptor 10 (not shown) because the inner surface of eachannular corrugation contacts the end connector 10 in independentlysealed rings. Also the geometry of the corrugations provides a usefulincrease in sealing pressure and reduces the effects of diametrictolerances because the flexing of the angled walls transfers the hooploads from the rings over a wider range of interference fits. This alsoallows the cuff region (17, 18, 9) to be a similar thickness to thehelical corrugations of the conduit, thereby eliminating one of thereasons for the lower production speed attributed to cuff regions inprior art conduits, increasing productivity and reducing manufacturingcosts of this conduit.

The annular region 18 also reduces heat loss from the cuff region byimproving insulation due to the trapped air between the corrugations,the adaptor 10 (not shown) and the outer sheath. With particularreference to FIG. 7, the annular corrugation region 18 has angledchannels 19 formed in, or on, the annular sealing rings in at least onerow to allow the wires to step over each annular ring as they transitionalong the cuff region 18 towards the end of the cuff 9. In this way thewires can be routed to the end of the tube so that terminationconnections can be made without penetrating the sheath (not shown).

Preferred materials for manufacturing the medical tubing of theinvention are Linear Low Density Polyethylene (LLDPE), Low DensityPolyethylene (LDPE), Polypropylene (PP), Polyolefin Plastomer (POP),Ethylene Vinyl Acetate (EVA) or blends of these materials. PlasticisedPVC may also be a suitable material, but it is not as well accepted forenvironmental reasons.

Preferred materials for the heater wires are copper, aluminium or a PTC(positive temperature coefficient) type material. Aluminium is not asconductive as copper, but may be an economical choice even though thewire diameter is larger for the same resistance. While the appliedcircuit voltage is intrinsically safe (less than 50V), for corrosionresistance and best electrical safety in the event of the tube or sheathbeing damaged, the wire will ideally be self insulated, either by enamelcoating or anodising in the case of aluminium. Alternatively an extrudedplastic sheath can be fitted, to insulate the wires from thesurroundings.

Test Results

A computer model was used to demonstrate the effectiveness of theconduit constructions of the present invention. Different corrugationforms of an inspiratory tube were modeled in Ansys CFX to compareexpected condensate accumulation during extreme use conditions of 18° C.ambient temperature and high convective heat loss. At the inlet, acontinuous mass flow rate of 30 liters per minute at 37° C. was used anda convective heat transfer coefficient, h, of 50 W/m2° K at 18° C. wasapplied on the surface of the insulation sheath to account for heat lossto the environment. This assumption approximately simulates a conditionwhere cold air is blown over the surface of the tube from anair-conditioning vent for example.

The model analysis obtained the temperature at the outlet (Td) whichapproximates dew point when air is assumed to be at saturation. Theabsolute humidity, AH, was then calculated from the dew point andreference temperatures from the following equations:

$\begin{matrix}{P_{v} = {P_{v,{sat}} \times {\exp \left( {\frac{H_{v}}{R_{w}} \times \left( {\frac{1}{T_{ref}} - \frac{1}{T_{d}}} \right)} \right)}}} & (1) \\{{A\; H} = \frac{P_{v}}{T \times R_{w}}} & (2)\end{matrix}$

where Pv=vapor pressure

Pv,sat=reference saturation vapor pressure

Hv=latent heat of vaporization

Rw=gas constant for water vapor

Tref =reference temperature

Td=dew point temperature

The following tables summarize the boundary condition assumptions andthe material properties used in the model of a typical adult sizedbreathing tube.

Model Boundary Condition Asumptions Parameter Value Inlet AirTemperature, T_(air)_inlet 37° C. Humidifier Air Flow Rate 30 L/minReference Pressure, P_(ref) 1 atm Power 37 W Ambient Temperature(outside 18° C. tube), T_(ambient) Convective Heat Transfer Coefficient50 W/m²-° K (outside tube), h

Material Properties Thermal conductivity, Component W/m-° K Remarks Tube0.3 LLDPE Typical Sheath 0.3 LLDPE Typical Gap 0.0261 Air Inspired Air0.0533 Air (compensated for humidity)

The resulting calculated condensate build-up for different breathingtube configurations are presented in the tables below. Predicted resultswere calculated for non-heated embodiments and heated embodiments of thepresent invention as described.

The results above show that the expected condensation volume isrelatively insensitive to the pitch of the annular corrugations.Comparing the rounded annular corrugation tube with the dip in cresttube shows a significant reduction in condensation formation(approximately 10% improvement). Similarly, comparing the roundedannular corrugation with the spiral corrugation configuration shows asignificant improvement (approximately 19%). The results furtherdemonstrate that the performance enhancements from the spiralcorrugation and the dip in the crest are cumulative and result in a tubehaving significantly superior condensation performance.

The results for the heated tube above show that heating the tube walldirectly results in significantly better condensate performance comparedto a tube with an internal heating wire of the same power. Inparticular, comparing the spiral corrugation with a heater wire in thetrough with the same tube construction having an internal heater showsan enormous improvement in condensation performance (i.e. 106.6 g vs.23.5 g (approximately 78% improvement)).

Similarly, locating the heater wire in a dip in the crest resulted in17.3 g of condensate. This demonstrates a significant advantage inpositioning the heater wire in a dip in the crest of the spiralcorrugations.

The results further show that the best performing configuration is atube having a spiral corrugation including a dip in the crest andwherein a heater wire is located in both the dip in the crest and in thetroughs. The cumulative effect of direct wall heating and theelimination of stagnant gas flow by the spiral corrugations results inonly 15.8 g of condensate (compared to 184 g of condensate for anunheated tube with rounded annular corrugations).

All of the configurations shown in the tables include an externalinsulation sheath around the corrugated tubes. The spiral corrugationform contributes significantly to the reduction in condensationformation compared to annular corrugated tubes by promoting good mixingof the gases in the corrugation peak areas. This effect is significantin both heated and unheated configurations.

The term “substantially uniform” wall thickness corrugated tube, isintended to mean a tube having a corrugation profile wherein thelocation of an outer peak, for example, comprises the maximum outsideradius of the tube while also comprising the maximum inner radius of thetube. In addition, the location of an inner trough, for example,comprises the minimum inner and outer radius of the tube. This type oftube is typically formed from a substantially uniform thicknessextrusion that is subsequently corrugated. It will be appreciated thatthe subsequently formed corrugations may vary the measured wallthickness of the outer peak regions vs. inner the trough regions of thefinished tube. The ratio of minimum to maximum actual wall thickness mayvary as much as 1:1.5-3.0 for example, but still be defined as“substantially uniform”.

Component of an Insufflation System

Laparoscopic surgery, also called minimally invasive surgery (MIS), orkeyhole surgery, is a modern surgical technique in which operations inthe abdomen are performed through small incisions (usually 0.5-1.5 cm)as compared to larger incisions needed in traditional surgicalprocedures. Laparoscopic surgery includes operations within theabdominal or pelvic cavities.

In abdominal surgery, for example, the abdomen is usually insufflatedwith carbon dioxide gas to create a working and viewing space. The gasused is generally CO2 which is common to the human body and can beabsorbed by tissue and removed by the respiratory system. It is alsonon-flammable, which is important because electrosurgical devices arecommonly used in laparoscopic procedures. The use of these devices tendsto create surgical smoke in the working space due to burning of tissue.Smoke evacuation systems which use a discharge arm or limb are commonlyused to remove the smoke from the surgical site, so that a surgeon cansee what he or she is doing, and so that this potentially harmfulmaterial does not remain within the body cavity post-surgery.

A typical smoke evacuation system generally includes a trocar and acannula at the end to aid insertion into the operative site. The smokeexits the insufflated abdominal area through the discharge limb. Thedischarge limb may be attached to the end of a laparoscopic instrumentso as to provide evacuation close to the site where electrocautery takesplace. Usually, the gases and smoke from the body cavity are filteredthrough a filter to remove particulate matter before they are vented toatmosphere.

It has been common practice in laparoscopic surgery to use dry gases.However, it is also desirable for the CO2 or other insufflation gas tobe humidified before they are passed into the abdominal cavity. This canhelp prevent ‘drying out’ of the patient's internal organs, and candecrease the amount of time needed for recovery from surgery.

FIG. 4 shows a typical insufflation system 200 such as might be usedwith the present invention. The insufflation system 200 includes aninsufflator 201 that produces a stream of humidified insufflation gasesat a pressure above atmospheric for delivery into the patient'sabdominal or peritoneal cavity. The insufflator 201 includes a heaterbase 204 and humidifier chamber 203, with the chamber 203 in use incontact with the heater base 204 so that the heater base provides heatto the chamber. The insufflation gases are passed through the chamber203 so that they become humidified to an appropriate level of moisture.The system includes a delivery conduit that connects between thehumidification chamber 203 and the peritoneal cavity or surgical site.The conduit has a first end and second end, the first end beingconnected to the outlet of the humidification chamber 203 and receivinghumidified gases from the chamber 203. The second end of the conduit isplaced in the surgical site or peritoneal cavity and humidifiedinsufflation gases travel from the chamber 203, through the conduit andinto the surgical site to insufflate and expand the surgical site orperitoneal cavity. The system also includes a controller (not shown)that regulates the amount of humidity supplied to the gases bycontrolling the power supplied to the heater base 204.

The smoke evacuation system 202 comprises a discharge or exhaust limb205, a discharge assembly 207 and a filter 206. The discharge limb 205connects between the filter 206 and the discharge assembly 207, which inuse is located in or adjacent to the operative site. The discharge limb205 is a self-supporting conduit or tube (the conduit is capable ofsupporting its own weight without collapsing) with two open ends: anoperative site end and an outlet end is made of a breathable foamedmaterial as described in this specification.

When saturated gases pass out of the abdominal cavity, they contact thecooler walls of the discharge limb, which is normally around one metrein length or thereabouts and moisture in the gases tends to condenseonto the walls of the discharge limb or exhaust conduit. Water vapourcan also condense on the filter, which can saturate the filter and causeit to become blocked. This potentially causes an increase in backpressure and hinders the ability of the system to clear smoke.

The present medical tubing as described above with reference tobreathing tubes, is also suitable for application in the delivery limbof a surgical humidification system. In particular, the medical tubingof the present invention is appropriate for use in the evacuation orexhaust limb of a smoke evacuation system. The performance benefits ofthe tubing are a result of the improved rainout performance (i.e. lesscondensation forming) of the tubes of the present invention.

Other

It is anticipated that the present invention will find other medicalapplications to which it is particularly suited. Any application whereconsistent heating of tubing conveying a humid gas in order to reducethe formation of condensation could benefit from the low cost andefficient heating of the present invention.

The foregoing description of the inventions includes preferred formsthereof. Modifications may be made thereto without departing from thescope of the invention. The disclosures and the descriptions herein arepurely illustrative and are not intended to be in any sense limiting.

1. A component comprising: a helically corrugated tube wherein thecorrugation profile comprises alternating outer crests and innertroughs, a heater wire associated with said outer crests, wherein eachsaid outer crest comprises a peak region, and the peak rels includelocal troughs comprising a small inward dip, and said heater wireassociated with said outer crests is located within said dip.
 2. Acomponent as claimed in claim 1, wherein said tube has a substantiallyuniform wall thickness.
 3. A component as claimed in claim 1, whereinsaid tube has a maximum wall thickness not exceeding 3 times the minimumwall thickness.
 4. A component as claimed in claim 1, wherein said outercrests correspond to a location of maximum inner radius and maximumouter radius of said tube, and said inner troughs correspond to alocation of minimum inner radius and minimum outer radius of said tube.5. (canceled)
 6. A component as claimed in claim 1, wherein said tubeincludes an outer sheath supported on said outer crests.
 7. A componentas claimed in claim 6, wherein said outer sheath traps air betweenadjacent outer crests.
 8. A component as claimed in claim 6, whereinsaid outer sheath restrains said heater wire associated with said outercrests in said local trough.
 9. A component as claimed in claim 1,wherein said helically corrugated tube includes multiple helixcorrugations.
 10. A component as claimed in claim 1, wherein saidcomponent further comprises a heater wire associated with said innertroughs.
 11. A component as claimed in claim 10, wherein said heaterwire associated with said inner troughs has a different heating densitythan said heater wire associated with said outer crests.
 12. A componentas claimed in claim 11, wherein said heater wire associated with saidinner troughs has a lower heating density than said heater wireassociated with said outer crests.
 13. A component as claimed in claim1, wherein said helically corrugated tube has a varying helix pitch. 14.A component as claimed in claim 13, wherein said helically corrugatedtube has a continuously variable helix pitch.
 15. A component as claimedin claim 1, wherein said component is one of: a conduit for use in atleast part of the exhaust arm of an insufflation system, a breathingtube for use in a breathing circuit and a catheter mount or tube forconnection to a patient interface.
 16. (canceled)
 17. (canceled)
 18. Amedical circuit tube as claimed in claim 1, wherein said tube isflexible as defined by passing the test for increase in flow resistancewith bending according to ISO
 5367. 19. A component as claimed in claim1, wherein said tube is an extruded corrugated tube.
 20. A component asclaimed in claim 1, wherein said tube is a breathing tube and isterminated by a first connector at an inlet and a second connector at anoutlet, and wherein only one gases passageway is provided the lengthbetween said inlet connector and said outlet connector.
 21. A componentas claimed in claim 1, wherein at least at one end of said tube is acorrugation transition region wherein said helical corrugationstransition to a substantially annular corrugation.
 22. A component asclaimed in claim 21, wherein each end of said tube includes acorrugation transition region where said helical corrugations transitionto a substantially annular corrugation. 23-40. (canceled)
 41. A methodof forming a component comprising: extruding a tube, passing saidextruded tube into a corrugator and forming corrugations in saidextruded tube having a corrugation profile comprising alternating outercrests and inner troughs, and wherein each said outer crest comprises apeak region, and the peak regions include local troughs comprising asmall inward dip, wherein said corrugations are helical, and whereinsaid method further comprises a step of winding at least one heater wireinto said local trough.
 42. (canceled)
 43. (canceled)
 44. A method offorming a component as claimed in claim claim 41, wherein said methodfurther comprises applying an outer sheath over said component.
 45. Amethod of forming a component as claimed in claim 44, wherein said stepof applying said sheath comprises extruding a sheath over saidcomponent.
 46. A method of forming a component as claimed in claim 41,wherein said extruded tube has a substantially uniform wall thickness atthe time of corrugating.
 47. A method of forming a component as claimedin claim 41, wherein said outer crests correspond to a location ofmaximum inner radius and maximum outer radius of said component, andsaid inner troughs correspond to a location of minimum inner radius andminimum outer radius of said component.
 48. A method of forming acomponent as claimed in claim 41, wherein said helically corrugatedcomponent includes multiple helix corrugations.
 49. A method of forminga component as claimed in claim 41, wherein said method furthercomprises a step of winding at least one heater wire into said innertroughs.
 50. A method of forming a component as claimed in claim 49,wherein said heater wire associated with said inner troughs has adifferent heating density than said heater wire associated with saidouter crests.
 51. A method of forming a component as claimed in claim50, wherein said heater wire associated with said inner troughs has alower heating density than said heater wire associated with said outercrests.
 52. A method of forming a component as claimed in claim 41,wherein said helically corrugated component has a varying helix pitch.53. A method of forming a component as claimed in claim 52, wherein saidhelically corrugated component has a continuously variable helix pitch.54. A method of forming a component as claimed in claim 41, wherein saidtube is flexible as defined by passing the test for increase in flowresistance with bending according to ISO
 5367. 55. A method of forming acomponent as claimed in claim 41, wherein said method further comprisesterminating a first end with a first connector, and terminating a secondend with a second connector, and wherein only one gases passageway isformed between said first connector and said second connector.
 56. Amethod of forming a component as claimed in claim 55, wherein said stepof forming said corrugations includes forming a transition region ateach end of said component, and wherein said helical corrugationstransition to a substantially annular corrugation in the vicinity ofsaid first and second connector respectively.
 57. (canceled) 58.(canceled)